GAS consuming?

[RallyJet2006]

I've noticed mine go drastically down on my last fill up as I can see my needle drop after going in 15 mile increments. I've only filled the car twice since I've bought it a few weeks ago and got 300 - 310. But with my current tank I'm at 100 miles at a bit over half tank. I do half city and hwy, but this seems to be a drastic drop. I'll monitor it for the rest of the tank an my next fill. If no improvements, I will try the plugs, fuel filter and vacuum lines as suggested.

Regards,

John

[angel318ti]

I'm right on track for 320-350 on this tank. Using 87 Octane. Old plugs and wires.

[ClutchJones]

I recently had a dip in my mileage and am struggling to understand why...
I was able to get extended warranty coverage for a bad catalytic converter ($0 at the DEALERSHIP...WOW... Thanks to 318ti.org users who made me aware of the extension!)
At the time, I was advised by my regular mechanic to go ahead and change the muffler as well as the two O2 sensors. Fine and good, since I didn't have to pay for the $1000 cat, why not?
Well, immediately after picking the car up, I knew there were problems. My horsepower and torque were badly off and the gas pedal just felt soft. In addition, the car dropped from about 27mpg city to 23.5 in just one tank of gas.
After reading some old threads here about the Stromburg exhaust deal several members went through, I decided to go back to my original stock muffler. This has mostly fixed my torque and horsepower issue. I feel like I've got my old car back again. However, the gas mileage has not recovered and may have even gotten worse.
The fuel filter was replaced less than 20k ago, as well as the spark plugs. I replaced the TPS within that same time frame, but have not replaced any hoses or the ICV.
Someone mentioned in the thread about the exhaust that these cars automatically adjust fuel delivery mixes over a few drive cycles. So, I'm hoping that after another tank or two it will level out. That is unless someone else has another suggestion?
I just paid my car off and have been thinking about mods, but after this muffler thing I'm thinking it might be better to just keep it stock all the way (save for some foglights or easy things like that).
BTW... I have an automatic and I run 93 octane always and the occasional bottle of injector cleaner.

[Mallard]

changing of lambda sensors / O2 sensors may cause the dme to read signals wrongly for a short period, i noticed exactly the same symptoms when i swapped mine.

in the first posters case, it may be a faulty lambda, fauly AFM / MAF, damaged induction bellows (from airbox to TB) or lambda / O2 sensor.

Take the car to have a fault code reading, they will test the O2 sensor anyway, and you should be able to see how serious the problem is.

i was getting "433 fault readings in 60 seconds @ 92 deg. celcius"

not a bad problem considering the DME - ECU normally makes over 20,000 read and correct calculations a minute..

but i changed it anyway

[Triple_A]

im always getting about 350-375 i do alot of HW driving and always have the needle pinned at 80, and i still get 30-32.5 combined mpg (flux due to heater/AC useage) i got a full tune-up < 10,000 miles ago and always use ELF full sythetic for oil change. are you burning any oil? consuming too much coolant? check your plugs and see if they have a white build-up on it, you might have to replace a gasket. i had to replace mine, really easy job.

[zboot]

I usually get around 375-400 but this last cycle, I'm barely making 300. I know I've been a lot more heavy footed lately but this is ridiculous.

[JPerfect]

Yeah, I get about 300 miles on a tank city driving.

When I go to the shore or so, I can get over 400.

And yes, i do like to push her a little bit... maybe more than that... hah